Many high speed rotary machines, such as dynamoelectric machines or turbines, employ thrust bearings to control or counteract thrust applied to the rotary components of such machines along the axis of rotation of their rotary parts. Conventional thrust bearings rely upon contact between relatively moving parts to absorb such forces.
However, as the angular velocity at the surface of the rotating element increases, either as a result of increased rotational velocity, increased diameter of the journalled element, or both, it is desirable to have a dry bearing with no contacting parts to minimize or eliminate inefficiencies in operation. As rotational speeds increase, it is desirable to have a dry bearing with no contacting parts to remove inefficiencies in operation.
To eliminate or otherwise minimize the losses caused by such efficiencies, resort has been had to magnetic thrust bearings. As is well known, magnetic thrust bearings typically employ a disc made of ferromagnetic material that is connected to the rotary part of the machine to rotate therewith. A pair of armatures, one on each side of the disc, generate a controlled magnetic field for the purpose of centering the disc between the armatures without actually contacting the armatures. That is to say, the disc is spaced from the armatures by small air gaps, and thus, the only friction involved is so-called "windage" at the air gaps.
Location sensors in the machine determine the axial position of the rotary component and through conventional control circuitry, provide controlled electrical power to the two armatures to attain the desired magnetic fields.
Such magnetic bearings work well for their intended purpose. However, since by their very nature, they are well suited for use in high speed applications, high stresses exist during operation of the machine in the magnetic thrust bearing disc. Should such stresses reach levels of sufficient magnitude as to cause partial or total failure of the magnetic thrust bearing, failure, even catastrophic failure, of the high speed machine with which the thrust bearing is used may result to minimize the stress the prior art has resorted to so-called "stepped rotor" configurations. However, this often results in a reduction in the magnetic force available to achieve separation of relatively rotating components. This in turn may require the use of larger magnetic bearings, adding weight and volume to the machine. It may also increase power requirements for powering the magnets of the bearings.
The present invention is directed to reducing stresses in magnetic thrust bearings used in such high speed rotary machines.